The guild I'm in, Temple Of Sutek (owner = jesadomasochistic), is a private guild, although we accept anyone. The reason it is private it because we're a VERY active guild, and if we feel that a new member is not active enough after the month long trial period, then they're gone.
We're a Lost-Desert themed guild, but that's pretty much just the layout.
We've got some contests that are run weekly, though you must be a member for a week before you can take part (another kind of 'pledge' for new members). As I said before, we're VERY active, and that's what we try to use to get us members.
If you're interested, please PM me or neomail me on "simsman24000" on Neopets.